Super Simple iPod FM Transmitter

FM transmitters can be complicated to build, but not this one — this iPod FM transmitter about the easiest you can possibly make. And though the science of radio is well understood, there’s a magical, emotional quality about it that we don’t often stop to appreciate. You will not forget the first time you pick up a transmission broadcast from a device you soldered together, yourself, from a few bits of copper, carbon, plastic, and wire.

I am indebted to Jim and Kat of Sonodrome for first introducing me to that experience, through this very circuit, which I first built on a pre-etched PCB from a kit they offered for sale as recently as 2011.

This design was originally popularized by Japanese multimedia artist Tetsuo Kogawa. The circuit itself is a slight variation on Kogawa’s simplest FM transmitter design, and the method of building it is sometimes referred to as “Manhattan style.” It uses a piece of copper-clad circuit board but, rather than etching the circuit traces through the copper layer, a large piece of continuously-plated board is used to make all the circuit’s ground connections, and small sections of plated board are glued to the surface to form nodes or “pads” that are insulated from ground. Besides being a convenient way to assemble circuits using minimal tools, this building method encourages you to think about circuits in an interesting way — as groups of connections that are either grounded or “floating above” ground.

This transmitter uses ten on-board components and will transmit a monaural audio signal about 30 feet. It is possible to extend that range by adding an antenna, and Mr. Kogawa’s website has more information about how to do that.

NOTE: Depending on where you live, operating an FM transmitter — even a very short-range one like this — may be illegal without a license. Unless you attach an antenna, it’s very unlikely that anyone will notice or complain about any transmissions you may make with this device. On the other hand, it’s very difficult to predict, before construction is complete, just where on the FM band this transmitter will broadcast. Use due caution during testing, and make sure you understand the law in your area before attaching the battery.

Step #1: Form the coil.

Strip about 4" of 18AWG solid copper wire and wind 4 turns around the threads of a 1/4-20 bolt.

Turn the coiled wire off the bolt as if you're unthreading a nut, and clip each lead to about 1cm.

Bend little "feet" on the ends of the leads and adjust them so the coil will stand upright.

Holding a pair of pliers in each hand, grab the coil's leads and stretch it evenly along its length until the feet are 12mm apart on center. You may need to even out the coil spacing with a screwdriver or other tool.

Step #2: Cut the board.

Use a straightedge, a utility knife, and the edge of a table to score and snap a 5cm × 4cm rectangle from the copper-clad board. This will be your ground plane.

Score and snap a 5mm × 5cm strip of copper-clad board, then score it crosswise at 5mm increments. Snap along these lines, with pliers, to create several 5mm × 5mm "pads." You only need 5, but you may want to make a couple extra.

Smooth the corners and edges of the ground plane and the pads with a small file. Be especially careful to remove any sharp copper burrs that might cause cuts on handling.

Step #3: Mount the coil.

Apply a small drop of cyanoacrylate glue to the underside of one of the pads. It doesn't take much. Use tweezers or small pliers to carefully position it in the center of the ground plane. Wait a few seconds for the glue to set.

Glue a second pad to the board, above and to the left of the first, along a line running at about 135° with respect to the long centerline of the board, as shown. Position the second pad along this line so that there's about 12mm between the centers of the first and second pads. Wait a few seconds for the glue to set.

Solder the coil across the 2 pads as shown. This will be easiest if you pre-tin the surface of each pad, and both coil feet, before applying heat to reflow the solder and join the tinned areas.

Step #4: Add capacitor C3 and resistor R2.

Solder a 0.01μF ceramic disk capacitor (C3) between pad 2 and the ground plane, and trim away any excess leads. It doesn't especially matter where you connect to the ground plane, for this or any other connection in the project.

Glue pad 3 to the board somewhere below and to the left of pad 2, as shown. You want enough space between pads 2 and 3 to fit the body of a 1/4W resistor.

Step #5: Add the electrolytic cap, resistor R1, and capacitor C2.

Glue pad 4 to the ground plane just to the left of pad 3. Space the pads to match the lead spacing on your electrolytic capacitor. Solder the electrolytic cap (C1) between pads 3 and 4, making sure the negative (–) lead is connected to pad 4.

Solder a 10K resistor (R1) between pad 3 and ground.

Solder a 0.01μF ceramic disk capacitor (C2) in parallel to the 10K resistor between pad 3 and ground.

Step #7: Add the 10pF caps, resistor R3, and the battery clip.

Solder one 10pF ceramic disk cap (C5) across the transistor's collector and emitter, (i.e. between pads 1 and 5), and a second 10pF ceramic disk cap (C4) between pad 1 and the ground plane. Trim any excess leads.

NOTE: For more convenient adjustment of the transmitting frequency, replace the 10pF capacitor (C4) between pad 1 and ground with a 20pF variable or "trim" cap. If you use a variable cap, the frequency can be adjusted simply by turning the trimmer shaft with a small screwdriver.

Solder a 470Ω resistor between pad 5 and the ground plane. Trim any excess leads.

Connect a 9V battery clip to the board, as shown, by soldering the red lead to pad 2 and the black lead to the ground plane.

Step #8: Attach the phone plug.

Unscrew the threaded housing from the tip-shield (TS) mono phone plug and set it aside. Solder a 4" length of red stranded wire to the center "tip" contact, and a 4" length of black stranded wire to the outer "shield" contact.

The shield contact has built-in prongs that can be crimped over onto the wires to provide strain relief for the solder connections. Use small pliers to fold these prongs over and crimp the wires beneath them, being careful not to crimp so hard you damage the wire insulation, bend the tip contact onto the shield contact, or otherwise short the 2 connections.

Slip the threaded housing over the wires and tighten it onto the plug threads again. Solder the free end of the red wire to pad 4, and the free end of the black wire to the ground plane.

Step #9: Tune it up!

Attach your 9V battery to the battery clip and insert the phone plug into an audio source like an MP3 player or smartphone. Start a song or other easily-recognizable audio track playing, then turn on your radio and scan through the FM band to locate the transmission.

TIPS:

Start with your receiver right next to the transmitter.

A digital tuner with precision down to 0.01MHz may be helpful.

Be patient and careful. Scanning is a bit tedious, but if you get impatient you may miss the signal altogether and mistakenly believe the transmitter isn't working.

If you scan the entire band and can't locate your signal, try changing the orientation of your receiver's antenna with respect to the board and scanning again.

It's best to run your audio source on battery power when you are first isolating the transmitting frequency. If you have to run it from mains power, make sure electrically noisy devices like fluorescent lights, TVs, and computer monitors are not active on the same circuit at the time.

You can tune the transmitting frequency by changing the spacing between turns in the coil. Closing the spacing will lower the transmitting frequency, while opening it up will raise the transmitting frequency. You can also use a variable capacitor for tuning (see Step 7).

Step #10: Mount the battery.

NOTE: This transmitter design needs very clean, smooth power, which is one of the reasons we choose to run it from a battery. Power from a "wall wart" or other AC adapter is smooth enough for most DC applications, but not for this radio transmitter. Using an AC adapter to power this transmitter is likely to cause the signal to be too noisy to use.

Use scissors to cut a strip of hook-and-loop fastener (velcro) tape to fit the length of your 9V battery.

Separate the hook and loop sides of the tape, remove the backing from each, and apply the hook (scratchy) side to the bottom of the transmitter board. Apply the loop (fuzzy) side to one of the battery's 2 largest faces.

Attach the transmitter to the battery using the velcro during use. When depleted, the battery can be removed and separated from the transmitter for recharging.

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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chuck

Cool circuit. This has a lot of potential for serious fun.
Throw a silent rave- with a small transmitter and antenna you can broadcast music to your party. Have your guests bring headphone radios and have a silent dance floor. Bonus points for broadcasting different music styles on different frequencies- it looks super cool to have folks dancing at different speeds and styles.
Do a pirate drive-in. Use a digital projector and a laptop to show a movie on a conveniently placed wall in an empty parking lot. Broadcast the audio over the radio transmitter, invite your friends and re-live the glory days of drive-in theaters.
Create walking tours and locational radio art. Build several transmitters on the same frequency. Set them in an area or along a path. Use the individual transmitters to broadcast parts of a story tied to the location, describe sites along a walking tour or broadcast a location specific ‘soundtrack’ to your park or campus. As the listener moves along the path or area they pick up the transmitters in succession. Set up a spatially connected choose-your-own adventure story in your neighborhood where route choices affect the story being broadcast. Depending on how far apart you space them you can get glitchy signal overlaps and noisy resonance and things.
The FCC doesn’t really care about small hobby circuits like this as long as there are no complaints. With less people listening to radio or watching broadcast television, there’s little chance of causing interference that will lead to complaints. Don’t be rude or stupid, avoid large or weird antennas and don’t try to be the next Radio Caroline and everything will be cool.

Have used them regularly for art installations and within the house as a wireless speaker system, great fun!

David

the law is the same every where, because it is a Federal Law, that says what you can use to broadcast, and that you must be licensed to send voice over the air, would expect that data would fall under the same category. This from first hand knowledge, I built an FM (may be was AM back in the day, think this was before FM) I sold it to a friend and he set up his own neighborhood radio station, and before he knew it the FCC was knocking on his door….lol

willnonya

You assume everyone is in the US.

ibrahim

I want to know how a FM transmitter works. Where can I find information on that.

I found some good information on the FCC website concerning low power radio transmission. It looks like that from standpoint of the FCC that this device would fall into the “Part 15 Devices” category and not require a license.

I would assume that the FM transmitters that you buy in the store to play audio from a media player through your car radio (for cars that do not have an AUX input) would also fall into this category.

ahoule

how do you set the frequency

TerryT

The frequency depends on the inductance of the coil and the value of the 10pf capacitors. The easiest way to adjust the frequency, for example to move away from a strong local broadcaster, is to slightly squeeze or stretch the coil.

S_Hennig

Thanks for reviving some memories. Decades ago I built lot’s of prototypes that way. The only thing I did differently: I used a Dremel to make isolated pads instead of glueing bits of PCB. That way I did not have to wait for the glue to set. Cheap and easy and works up to VHF (well, obviously ;-)

stinker

i better want to know how this circuit is working…

stub

On a stereo jack, the tip of the jack carries the right channel and the ring of the jack carries the left channel. Would it be better to use a stereo plug (tip/ring/sleeve) and solder the tip and ring together in the plug, rather than allowing the mono plug to connect the left channel to ground in the mp3 player’s jack?

Shawn

Great tutorial, but I think you should include HOW the circuit works as well. It would be nice to see the explanation behind the design of the project.

I haven’t seen ANY replies from the author here. So I thought I’d chime in. I think an electret mic requires some power. Also the mic signal will be weak and might require some (pre) amplification. But I may be wrong about that.

Elmo

We have tried to put an electret microphone, but the sound quality is not good, but you will hear a significant sound coming out of the receiver .

deojo

please share your result here, if you get way to fix it. :D

Levi

I put this together and for some reason I still can’t find it on the radio and my 9v seems to get hot pretty fast. Any advice would be great thanks!!

John

I imagine that you have shorted the battery’s red and black lead somehow. Use an ohm meter or continuity checker between the terminals of the battery plug (with the battery unplugged). You should see a very high resistance value or an open. If not then check your wiring. Watch for solder shots from the pads to the ground plane.

John

Why use a mono plug? I understand that the transmitter will only transmit monophonically, but with a mono plug you will only transmit one channel from the MP3 player (left or right but not both) loosing part of the music. The better choice is to use a stereo plug and run the red wire to both the left and right pins (black wire to ground as shown). Then you get both channels transmitted!﻿

scott

i built the transmitter as well, how does the amount of turns on the coil affect the signal ….is more better or less

AJ

I’ve built three of them and none of them worked. I triple checked everything and I connected everything correctly. I did use double-sided copper as that was all radioshack had. Is that OK? Troubleshooting?

AJ

When I touch one end of the coil I can sometimes get a clear signal to 107.3. Please help.

Pvt. Parts

Yes I had this but on the transistor E leg, Turs out C2 ground leg did not get solderd well… I did get signals in 89.7 and 99.9 but it is not clear at all :(

Pvt. Parts

Any suggestions on how to make it more clear on sound? when just voice is getting transmitted no problem, but when the music comes in it sounds like a chainsaw

Keen

lessen the volume of the input audio signal to get a more clear sound.

Seemed like the copper ground plate was pretty specific. Do you think your breadboard is functioning the same way (ground-plate-wise)?

Vish

I want to connect this transmitter to the tv rca output and i tried it but its not working plz help me…..
Thanx

Dwayne

You should try making an IC type transmitter.

Tibi

I build a lot of these transmitters when I was a kid. Had a lot of fun playing with it baut it sucks that they’re so sensible to changes in temperature and mechanical shock. Every time you touch it or even get close to it, it changes frequency and you have to tune in to find the broadcast. Having a crystal in the equation makes it stable but those circuits are a lot more complicated to build.

can an Inductor of predefined value of certain inductance be used instead of the coil? I couldn’t find an 18 gauge solid copper wire but I have a 1mm diameter copper wire, will that work?
If an inductor can be placed instead of a coil what value must it have?
Thank You

The text suggest that an AC power source would be too noisy for this, what would you think about using an automotive 12v dc source or USB to power this?

vish

I want to connect this transmitter to the tv rca output and i tried it but its not working plz help me…..

Todd

Could this design be adapted to broadcast in stereo?

Andrzej

I have question to you. How can I connect antena to this circut. Thanks.
P.S awesome project

Toad of Toad Hall

Very interesting. Quite illegal, of course.
But, oh dear, didn’t they teach you to look after your tools?

nusak

i would like to interested so much !! how can we use the mic test the sound ??

Christian Juth

Can I use a 0.01 uF mylar capacitor? I know the charge and discharge are slower but will it work? The voltage rating is above the 9v that the circuit can provide so it should be fine. But will the slower discharge matter?

lim

could you can show all details for the resistor ! Cuz i final year wan to do it

EchaaBoy Shehroz

transistor value ?

Jake

It has been very hard for me to find solid copper in my area can I use tinned copper instead?

This is fantastic. Thank you very much for posting it. It works very well. I use it in the car in order to connect my phone to the radio so i can play whatever i want. Without antenna the range is just 1 or 2 meters so it doesn’t cause any interference at all. When i attached an 82cm long copper wire as an antenna the range went up to 100m or so. I may connect the circuit to the 12V electrical circuit of the car. I assume it will just increase the range.

Thilina Jayasingha

Is it works realy.i’m not make it. But i wanto know what freaquency can heard you?plz reply me as soon as possible.

WH

yes, it works but the frequency is sensitive. In prototype board i
first got 91MHz then i built the circuit on copper board and the freq
went down to 86MHz which is out of the FM range. In my experience the frequency also depends on the battery level and whether or not an antenna (that can be an 80cm long copper wire) is connected to the output. I checked the output freq with a high freq oscilloscope.
If you use a 2-22pF variable capacitor in place of C5 you can change the output freq. The less the capacitance the higher the output frequency but the less the output performance will be. You can compensate the performance drop by adding an antenna but it affects the freq a little.

Kathan Patel

can you plz sent me the pic bcs i had made it but it is not working

WH

Sorry I built it on a prototype board and because i didn’t use it i took it apart so i don’t have a picture. I assume the frequency may be out of range. try different capacitors in place of C5 a variable 2-22pf capacitor is good. or variable resistance in R3. You can change the length of the coil too if you press it or stretch it. The best if you have an oscilloscope because you can measure the output frequency and you can see the effect on the output frequency as you change certain parameters in the circuit

WH

I found an image on my computer

Kathan Patel

sir i had done it is working but sound is too noisy and on all frequncey my chanel is tuned means on all frequency my song is playing

WH

i’m no sure why this is happening. try to get help on a ham radio forum. you will find people there who design and build radios.

Koby

this is awesome I’m going to make one. But where would you connect the antenna?

Zidane Tribal

you would hook up the antenna to the emitter of the transistor. at least thats what the diagram shows and how i have it hooked up. havent tested the distance yet.

noahstewart

Has anyone created a stereo version of this?

Shrivardhan Kantharia

yes i have but it’s not working

Zidane Tribal

i made this myself, but it seems that with a 9v battery i can only use volume 36 at most without significant distortion. i dont know much about transistors and their voltage ratings, but i hooked it up using 18 volts and it was running fine and i could use a higher input voltage as well. hoever, after about an hour the 2 9v batteries were warm – how would i check the current draw? i tried the amp probe on my meter but it didnt work.

-FireControlman 2nd Class USN

current draw would be P/E. power divided by voltage, so you have to do the math and find the current through the collector and go from there

Amitabh Songara

sir
can you tell how we can change the frequency

WH

you can change the frequency if you replace C5 10pF capacitor with a 2-22pF variable capacitor.

as far as i see the wire length is calculated from the diameter of the wire on the page you recommend but it should be given as 12mm. They actually mixed up the wire length and coils length.
Check what happens if you input the coils which means the turns as 4 and the diameter of wire (k) as 1.02 (18AWG). The wire length is calculated as coils x k = 4 x 1.02 = 4.08 (This should be 12mm!!!). What they call coils length is wrong because it’s the length of the wire and it is calculated as D x PI x Coils = 6.35 x 3.14 x 4 = 79.9mm

Archy

Worked nice 4me m8…
Great i did some half shematics and it works!!!

Nick Vanderplop

or any other variable capacitor with a similar range

Benjamin Bartels

How would you replace a ceramic capacitor with a variable capacitor?

WH

You can use a 2 pin trimmer capacitor or if you use a 3 pin trimmer capacitor just use 2 pins of the 3.

Benjamin Bartels

Which two pins of the three should I use?

WH

the capacitor has 2 isolated plates. 1 pin is connected to one of the plates and i believe that the other 2 are connected to the other plate. You can test with an ohm meter to find out which ones are connected to separate plates because the resistance is infinite between them so you can try those. One of your pins will be the one that is connected to the screw. If that’s a copper screw then there shouldn’t be any resistance between the screw and one of the pins. I would try that anyway.

Phương Đăng Trần Thành

How can i change the frequency by changing the coil because in my country, trimcap is not available

michael george

you can change the coil by using a variable coil or changing the number of turns or length or diameter of your old coil

Seth Nintendo

How many watts?

-FireControlman 2nd Class USN

P=IE

Finnley

I could not get mine to work do you have any suggestions

davidson

can we see yours?

Saurabh Singh

is any substitution of 2N3904 transistor.If exists pls reply.

Gareth Andrews

2N3904 / BC547 / PN2222 / 2N4401 are all NPN transistors,

don’t know if they’ll work but its worth a try :)

Fokko Perton

Bc547 or 537 both work a charm, they’re more easily gettable in my case.

concerned_legal_citizen

Sean, I just finished building the fm transmitter. I did get it to work, however, it is very sensitive touching any of the components on the board. I added a 3 inch antenna. To get the transmitter to work, I have to adjust the coil and then back away about 6 feet to hear it working. Is the one you built this sensitive to frequency changes and proximity to your body?

Declan Embury

would it be possible to connect i mic directly into the transmitter?

-FireControlman 2nd Class USN

yes absolutely, it will take the same input audio frequencies that you apply with your voice the same as it would music from a phone.
-FireControlman 2nd Class USN

-FireControlman 2nd Class USN

I love this stuff, although im having trouble breaking down the signal flow, and description of each component and how they are ‘reacting’ to each other.

sajjad

Hi, I have build this circuit, but it does not work
is there anybody to help me with that?
if yes, I will send the picture of the circuit that I have build it on the bread board.
To tell you the truth, I dont know even it works, or not? (I mean maybe I have the wrong frequency to be catch with FM)

sajjad

I found the mistake
there was an error in my transistor. I simply plugged it reverse on the bread board. ;)))
when it worked, it’s frequency was about 91 KHz
Thanks for your great & simple project

by replacing the audiojack with a microphone, will i need to an additional component to transmit my voice? thank you

Gareth Andrews

“yes absolutely, it will take the same input audio frequencies that you apply with your voice the same as it would music from a phone.”
-FireControlman 2nd Class USN

all ready answered :P

Vishnu Suresh

can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

Gareth Andrews

YES you can!, as long as the circuit connection are the same it’ll work, what you talking about is a “rat’s nest circuit”, i do this allot as i too cant get copper clad where i stay

Vishnu Suresh

can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

caswell

Hi, I have built the super simple radio transmitter, it works but the signal is too noisy or scratchy, what can I do to enhance, I suspect my coil is the problem as it is not even, it is also found too low in the FM spectrum, how can I move it up to the mix be range of the spectrum, thanks a lot, enjoyed building it……caswell

dqsdsq

doesnt work…wow…I tried everything… :c

michael george

1-Try to use a very long antenna such as : a dish of aluminum from the kitchen :D :) I’m not joking, I connected my antenna to a very big dish and it works.

2- check your connections, I’m sure you will find something wrong.

3- check your power supply ( battery or transformer ).

4- use another coil and capacitor ( L1 and C5 ) and it’s better to use variable capacitor and coil so that you can change the frequency and your radio may receive the new frequency. I think the old frequency is out of the range of your radio.

Vishnu Suresh

can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

michael george

This is an amazing circuit. it works properly :)
but it would be better if you explained the function of each component in details.
Would you tell me what the function of C4 is ?
Thanks in advance sir,

JP

Can I substitute the 18 gauge coper wire for something else because its hard to find where I live?

Annesha Roy

can anyone tell me the all parts name and specification…

Anup Upadhyaya

Where can I find the hardware used ? Can I find it inside a CD player? Or inside a Radio ?
P.S. : I am not a electronics student.

John Daniels

You could probably find it all in a radio, but any electronics parts store should have everything you need. Radio Shack is the traditional place to find this stuff in the US, but these days they’re hit and miss. Amazon.com probably has it but you might have to buy large quantities. You don’t have to be an electronics student if you just look at the numbers. Usually the voltage rating on these parts (for example 25v) is the maximum voltage you can apply. Since this uses a 9v battery, anything above 9v will be ok and anything lower than 9v could burn out. The resistance or capacitance rating is the number that you need to match (for example 103k on the resistor and 22uF on the capacitor). I hope this helps you find the right parts.

Yikes, I’m just noticing that you posted this a year ago. I hope this can still help you a little or anyone else just starting out.

adam kendrick

So if i used a 450v electrolytic capacitor in this circuit, will it be ok? I am using a 9v battery with these capacitor, like the video said.
Also, The list of materials says i need metal film resistors, I am using CF (carbon – film) resistors. One of the resistors I am using is only 1/2 a watt when it is supposed to be 1/4 a watt. Is this ok???

John Daniels

The 450v capacitor will work fine. The voltage on a capacitor is the maximum voltage it can handle. They can handle lower voltages, but they get physically bigger with higher voltage ratings. The resistors are going to work fine as well. They’re simply made of different materials, but as long as the maximum ratings are not exceeded, they should work ok. With resistors, the 1/2 watt is a higher power rating than the 1/4th watt. A 1/2 watt resistor can resist more power at a give voltage than a 1/4th watt resistor. They both can resist up to 1/4watt, but the 1/2 can go higher (up to 1/2 watt). Does that help?

Aman Raj

What is the exact dimension and specs of coil…. My circuit is not working

Aman Raj

Somebody. Please reply….. What could be the possible mistake

Atta Muhammad

Sir how to add antenna to this circuit … Thanx

Irfanuddin Shafi

Hey,
I couldn’t get 500v 0.01uF Capacitors, i got smaller(size) one of it(same value i.e, 0.01uF), stating AEC is it Okay? :O

jonas Biensack

jup, the 500V doesn’t matter, even a 16V will work

Irfanuddin Shafi

Thank you for your sincere reply. I’ve got another question, I have built the circuit, it works. But there’s a lot of noise and frequency changes often. Also, the sound is not clear.

jonas Biensack

How did you build it? Can you provide a picture of your work?

kind regards Jonas

Irfanuddin Shafi

I had built it on copper clad board.
Here’s the pictures

jonas Biensack

Not so bad at all, but why don’t use a smaller pcb like mentioned avove (5cm*5cm). And your soldering points are looking extremly bad (cold ones), make them new and test again.

Irfanuddin Shafi

Can you give me your email? I will contact through that.

ghggygh

at what frequency it transmits signal???????

Dhave Gatchalian

can i use bc548 transistor?

Clark

Will an aluminium foil covered board make any difference in performance when compared to copper clad board?

ASPACEMAN

Good question, anyone? I tried to get the pieces to connect to a scrap piece of copper pipe, but I think that’s advanced soldering.

Some DIY Copper board ideas!?

vaibhav

can i use my mobilephone as receiver??……and can i connect condenser microphone at the input of the same circuit instead of audio device??

atar

yes

Edwin Moses

can i use bc 547 or bc107?

jonas Biensack

yes

zubair

can i make it on bread board??

John

I made this on a breadboard witch did work, but it won’t transmitter like it did. I can barly hear the music and can’t find a set station for it. Could the transistor have broken or is it something else.

Aidan Payne

Where would I attach an antenna that has multiple connections, like on taken from an old radio?

Irfanuddin Shafi

One to capacitor c5 and the ground to ground plane.

santosh

can i make this project on a pcb

Irfanuddin Shafi

I’d suggest you to do it in Copper clad board.

Sam

can i use a single sided copper clad board

Irfanuddin Shafi

Yeah, the copper board acts as ground plane, and the pads are the ones that aren’t grounded.

Hi! i’d like to use this transmitter in order to communicate with another device wireless (i want to control a simple robot with an arduino connected to my pc that makes this transmitter send some signals with a different duration and another arduino that receives the signal through a receiver)… is it possible? can someone help me to build the receiver that operates at those frequences?

marco girardini

Hi! i’d like to use this FM transmitter in order to control a robot: i think I’ll control the transmitter through an arduino to send some different duration signal, so i could control all the motors just changing the duration of the signal. After that a receiver receives the signal and sends it to another arduino that controls the motors. Is it possible? can someone explain me how could i create a receiver that operates at the same frequences?

Sohit

how can i run a toy car using these radio signals

Hans Peter

Hey friends…I`m desperate cause sitting since one day and try to find the fault…i used a plugin panel to create it…but i cant find the frequency…is it possible to measure it with an oszilloscop?

Eric Melonakos

Does the actual number of turns on the coil matter? And does the size of the turns matter? I don’t have a 1/4-20 bolt. Also, what does 1-33 uF for C1 mean? I have a bag of electrolytic capacitors, but they each just have a single value (e.g. 33 uF). Thanks for any help you can give!

Nick Vanderplop

uF is the abbreviation for Pico-Ferads, where Ferad is a unit of how much power the capacitor can store, and pico means *10^-12, or in English, a decimal point with 12 zeros after it before the number. The person most likely meant by 1-33 uF that one with a capacitance anywhere between 1 and 33 uF ould work, or a pecial capacitor that is adjustable to accomadate more or less power.

ThisGuy…with2thumbs

Newbie here…but, are you saying that choosing a capacitor between this range will vary the power output, and thereby increasing range of the signal?

Nick Vanderplop

when i say “power” i am referring to the total power storage of the capacitor, not the output of the transmitter. What is made with the capacitor and the coil is knows as an oscillator, and a capacitor with higher capacitance charges slower (because it takes more power) and therefore lowers the frequency, and a capacitor with less capacitance charges quicker (because it takes less charge) and therefore makes the oscillator quicker. Neither directly affects the range.

ThisGuy…with2thumbs

Ahh…I get it now…thank you. So, then, I could use a varicap for this capacitor to alter the frequency, right? With regard to output power, how does one increase the power output of a transmitter? My initial thought would be to increase the wattage being supplied through the power source, but then I start thinking about the components and their limits. How would you, say, double the power output of the transmitter in this example?

Nick Vanderplop

simple: use a bigger transistor. That is the component that amplifies the power going to the antenna so it transmits more power than is going through the actual circuit itself. Strengthening that would strengthen your signal. Also, I strongly suggest an antenna (just a wire is fine) about 8 feet long. That makes the transmitter much more efficient.

ThisGuy…with2thumbs

Hmm…that never crossed my mind! I’ll definitely try that! If I wanted to measure the power output, I’m assuming I would measure it from the emitter side, but how? Would I just measure once for amperage, and then a slightly different way for voltage, thereby getting power? All I have is a multimeter. To take a stab at it…measure voltage from emitter to ground, and amperage inline immediately following the connection to the emitter? Thanks again for answering these questions. I’ve recently become facinated with how radios work.

Nick Vanderplop

to accurately measure the output of a radio you need special equipment as the power from the emitter to ground fluctuates as it transmits a signal. You could get very different readings based on what you are transmitting and how loud. That is one reason things like this exist:

ThisGuy…with2thumbs

Alright…thank you tons for your advice!

Hemanth

I am really happy that u posted this one . But is it possible to hook up a electret mic? Or antenna? If so where must I hook it up?? Pls reply as soon as possible because I want make this fm transmitter soon!!

Hemanth krishna

can i add a electret microphone and a antenna?? If so where the broad? How to connect it? Pls reply and i am exited for this project

Utsav Naha

If the transistor is pnp, will the postion of the tank L and C change?

Anil Yadav

Not working at all,but found some disturbances at 94.1,Can i use a 5mH Inductor in place of coil.
Tell me how to place the antenna

33uF=??????

Prathamesh Belnekar

any one can plse tell me where tu put the entinna

Naman Sachdeva

I had a go a making it.
From the initial component values, I was able to achieve oscillation around 136Mhz (as measured on my oscilloscope). The critical components that influence the frequency are the two 0.01uF (=10nF = 10,000pF = “103”pF) capacitors and the 4-turn (1/4 20 bolt former with #18 wire) inductor. While I used #16 wire, which will have influenced the inductance, I needed to alter these components in order to lower the resonant frequency of the carrier wave:
I used larger 0.1uF = 100nF = 100,000pF = “104”pF capacitors and I used 6-turns of the inductor, spaced out to roughly 16mm or so (I failed to measure this width, so tweak it if needed). As they say, ” your mileage may vary”.

With these larger oscillating components, the frequency was lowered to 99.65MHz as measured, and the results work well at 99.70MHz on the radio dial.

The transmitter is ‘rough’, but can be made to sound clearly. I needed an antenna from the ground plane to radiate enough power to overcome a stronger commercial station at 99.7FM. Hand-capacitance was strong too, so you might need to listen with some correct body positioning near the circuit.

Overall, a nice circuit as a demonstration, and with so few components, it offers a good learning tool to understand what is going on. However, I am still struggling to think through the processes and events in the circuit, so any comments on how this thing works are greatly appreciated!

raiden

can u plzzz tell me the priciple on which it works….plzzz explian the working of the model ……it is for my physics project ……..plzz reply fast

Praneeth Mv

I’ve not built this, but please can I know if i can connect a microphone/mic to it so that i can speak….?Thanks for any help.

MrJeppe

If i want to add the antenna, where i should solder that?

Advait

You would have to connect any piece of insulated wire to the emitter of the transistor. IF you connect that wire to a metal dish, then you will have some excellent range:)

Shaikh Nahal Maqsood

What I I Want To Recive Signals From a Wire ? PleaseReply Me I Am Not The Student If of Engeering But Its My Project Please Reply Me ?

JS7457

i make it and it so cool !! do it with a cooper board ! Very good quality for me !
102,5 Mhz ! I use a 0.05mm solid cooper wire, 4 turns !

Can you make a part list of this FM transmitter on Conrad please? I don’t now exactly what the parts means.

Thom Debruin

Can anyone make a parts list for me at Conrad or whatever.
i don’t understand the parts and don’t now which one i should choose.
please help me!!!

homerlaughlin

From that question, You’ll put an eye out. Get a little transmitter on ebay and forget it.

saiteja

Hi,
i am saiteja doing undergratuate degree.i have built the fm transmitter and when i sent the audio signal,we are not getting the output i.e.., audio signal which we get at a certain frequency.so please give me suggestions to work out the project.

Alberto Sánchez

Amazing project with great explanation, I am definitely trying it out! It is only missing a better explanation of how to add the antenna.

Peter

hi there. i’m trying to understand the values of all the components, can you publish the derivations of the circuit

emily

can u please explain what resistor r1 is and capacitor c2 are. in the materials they don’t tell us what those are can u baby the procedure steps to easier words

Jaso Salt

Is it possible to add a microphone?

Connor Bunz

Id imagine that you’d have to add some sort of amp to the mic, considering it probably doesn’t have any native power running through it

Nathanael Beall

Thats what i had thought to, i think another npn tranistor might work like this

vishwanath k

Sir ,
Instead of copper clad board i have used normal PCB i am not getting output in my circuit also i have used C1 as 0.01uf has variable capacitor is not available in my region .PLEASE TELL ME HOW TO GET OUTPUT …
thank you.

Eden Simpson

Hi I recently made one of these, for C1 i used 1uf. the input doesn’t need to be very loud for it to work. For lack of copper board i used the 3D approach as seen in the picture.
I used a BC547 as the transistor.

My one is 96.1 mhz but it only works if you hold the Antenna.?

javier

may be u have a bridge somewere, probably on ground, o you have not at all so you are instead when u touch it.

This worked perfectly. Tuned in around 90.1. One thing to share: stick with the specified NPN transistor specified. I tried a pwn222a and it did not work at all. Thanks to Make and Sean for their great work. You share so many enriching projects.

Shrivardhan Kantharia

i did but its not working. Can you tell me some tips or any precautions regarding construction of circuit

Advait

Do not change any of the parts and it should be working nicely.

nikola bojkovski

how can i make stereo transmitter ?

Joseph Irwin

Interesting!

Stuart Canfield

Hi, first off i want to thank Sean for this super simple circuit. Thank You :) At first i built this with a ball of wires, it was a bit chaotic, it tuned into 92fm with 10pf which was undesirable do to the fact it was on top of a station and didn’t come in good. I then put in a variable cap in place of it. This allowed me to get the full radio band with surprisingly good quality. After that i decided to take it a step further and designed a simple PCB board to put it on. I’m not sure if its because i mangled the wire a bit or the lack of Antenna, which i have made a spot for just haven’t tested it, But it does not come in as good as it did before i put it on a PCB. Thanks Again!

Here are some pictures of my project.(note this is only my second PCB/first circuit i have built so soldering and such is a bit choppy <.<)

Advait

Is the transmission supposed to be grainy and unclear? I am getting a very rough sound out of my fm radio. Also which electrolytic cap should I use? Does its capacitance matter? Can this project be done on a breadboard?
Thanks in advance.

Advait

Guys I have made the project now and it is quite stable except for the fact that the output is grainy. SOMETHING WEIRD I NOTICED IS THAT CHANGING THE ELECTROLYTIC CAP FROM 22 uf to 10uf DOESN’T EVEN CHANGE THE OUTPUT FREQUENCY! I don’t know how or why this happens, but when i changed the capacitors while while i was broadcasting something, i didn’t even have to tune the radio a bit to listen to it.
Could somebody please tell me how to make the transmission more clear. I want it to be as clear as an official radio station.
Thanks in advance

Advait

Also, I have made this project on a breadboard and have not at all changed the measures of the different capacitors or resistors. The only thing I have changed is that my inductor was wound around something thinner than 1/4 inch and is therefore of lesser diameter. I have tried to compensate that by giving 5 turns of wire. Also I don’t know the AWG thickness of the wire I have used. Does this, in any way, affect the sound quality? Please help me improve the sound quality of my circuit.

Advait

Hi

Advait

How can i improve the quality of the output? I have made the circuit on a breadboard. The only thing i changed is that i made my inductor of a diameter thinner than 1/4 inch and to compensate that i put in 5 turns of wire instead of 4.
The output is really grainy and unclear pls help me:)

Advait

Pls help this for a science project i need it fast

Advait

I am really sorry for thee repeated questions i have not done it purposely i just made this account yesterday and first when i asked some questions they werent showing up when i visited the page again and i kept on entering them out of confusion but now they seemed to have appeared i don’t know how this could have happened.
I am relly sorry

Sybe

Do you really need to use a ceramic disk capacitor for 0.01uF

Nathanael Beall

can i simply replace the jack with a 2 pin mic condensor?

Lukas

Amazing, am i the first to realise that it works just fine without any power/battery…
This meant i could make a tiny adapter for my phone to play music to any radio!

Gabriele

You can send me the schematic and components that you used? I I want a test for my phone.

Gaurav

Hey Lukas that was indeed remarkable.Would be great if you could please share this compact PCB component layout with us…

Lukas

Sorry I didn’t notice the comments.. To be honest, All i did was place all the components in a line as you can see in the picture. But I made sure that the components next to each other made connections in order to avoid too many jumper cables. I used a project board rather than a custom pcb. I just have to point out that the audio input provides enough power to emit a weak signal which i found can only be captured by more powerfull radios with a very low range of about 1m. However, this is pretty remarkable considering it does NOT REQUIRE a battery too work! Unfortunately i don’t remember and i dont have time to create the layout which i used to build the transmitter in the picture but give it a try! Play around with the layout.

Gaurav

Hi Lukas…thanks for taking time to reply.Can you please support by atleast clicking a TOP and Back Image of your assembly for my kind reference.

Also I am surprised when you say that this circuit doesn’t require any power as it works on a 9V battery !!!

I do not have any projects.You can check this website for some great projects….

Jcw608

I do not have a bolt that size is there any other common item I can use to make the coil?

Christian

Hi there i am christian from norway and i built a super simple fm transmitter. My problem is that it so much noise. I fond my signal on the radio but it is weak and too much noise. What can i do to get a better and not so noisy signal?
Thanks for all the help:-)

Gaurav Solanki

Hi, If the inductor value is 42.74nH and the capacitor C4 is 10pF as per the tank circuit equation the output frequency should be 243.45MHz (which is out of FM range).
What’s wrong with my argument?
Thanks in advance

prabhkaran malik

Can i substitute the ceramic capacitors with something else

ivan R

will changing the resistor values do anything?

Daniel Rico

It does work, I’m transmitting on (+ or -) 96.5 FM.

ADVICE: Use a multi meter to check for voltage drops across each circuit element (You don’t need to know what the number is supposed to be) you just need to see If an element does not have any voltage drop (aka its 0), at this location there is a problem and you should re-adjust the circuit appropriately there!

Be patient with the tuning, and remember to play a song that is EXTREMELY recognizable to you. I played Disney’s Hakuna Matata lol.

Cubeofcheese

I have 18 guage wire, but out is not solid, would it still work?

RonerCrisostomo Pacardo Ibarra

sir if i like to operate in 3v what component is change??? thanks

Pranjal Choudhury

hello sir, can u please explain the role each of the component in detail, i was thinking of making this transmitter as a school science project.

Hey, I actually made this fm transmitter for my school project but the problem with the transmitter is that it is emitting the input at every frequency so there is no particular frequency required and there is lot of noise while receiving the signal, so can anyone tell me how to solve the problem of frequency?

Peter Dactyl

You may be overdriving it. Turn the volume of the mp3 player down and the radio receiver volume up.

Indira Ganesan

does the receiver detect the new frequency we r broadcastig or it chooses the previously available fm radio station frequecy

Şhaň Đařež

were to add an antenna to make the frequency range long….????can we add an antenna…..!!!!!

Kathan Patel

sir i had made it but it is not working my all connections are perfact the only thing i has different is C1 as 1uF capacitor. plz suggest me what to do

Kathan Patel

thank you make team…….thank you so much done my project its just awsome ……got 40/40 marks in college project thanksssssss………..

rocketstrong

its very sensitive how would i stabalise it

DJ SAJUJA

Can u tell_
How to make fm radio transmitter
Can Listen any one on my council?? Please help me!

Jack

Hi could i use a Capacitor, ceramic disk, 30pF or 40pF to increase the frequency more or can i get a 15ph capacitor.

I tried to made two, but neither one is working… Please help me to solve the problem.. I don’t have any knowledge about electrical component.. I tried to search radio transmission by Android Phone’s Radio.. I used general wire for coil.. I want to build this.. :(

Hassan Tariq

can you please tell me , how do you design the values of capacitors , how to make a inductor and choose a transistor ?

Hi, I have built this transmitter with my students and it works great. Thanks for that!

I tried to demonstrate frequency-modulation, but I did’t succeed.
First my proceeding:
I gave a sinewave-signal of 1Hz on (and in a second experiment a sinwave in kHz range) into the input of the transmitter. The modulated signal was displayed with an induction-loop on an oscillocope. The carrier-frequency can easily be seen. I hoped to see, that in the 1Hz-case, the carrier-frequency would slowly vary with 1Hz. In case of the kHz-range, I hoped that the trigger of the oscilloscope would display a freeze frame, where the periode varies slowly. As told, both methods didn’t work.

Maybe the resolution of the oscillospe isn’t good enough. So I modified the transmitter and built in a coil with a higher inductivity, so that transmission-frequency is not in MHz-range, but in kHz-range. So the frequency-modulation should become clearer. But this didn’t work neither.

Do you have any tips for me for demonstrating frequency modulation?
I would be glad for any hints.
Thank you.

Bashar Khan

What if i use dot board?

Pares Malindi

What can you use instead of 18 AWG wire can’t find any?

Pares Malindi

I am struggling to find 18 AWG solid copper wire is there any alternatives?

Dim Pap

Hello i am ready to build the project but i want to use a not used Frequency is there any way I could change the Frequency in such a way to use the the 104 MHz Frequency

TECHnology FOBIA

i want the broad cast frequency to be 77.7 can any brilliant guy help me
my email[email protected]

please help me fast i am working on my school science fair

Vicky Sawant

Sir is it work on 5v supply? Plz explain :)

ISHA DEEP

What is the resonance frequency of the circuit?

Airra Basas

What is the propose of C1?

Thanks

XTwentyThree

Amazing! This was my first electronic circuit

Airra Basas

good day!, there is a noise? someone help me :/

Nagasainath Chowdary

How to use this for HAM radio (FOX HUNTING) in VHF BAND(144.00 to 146.00)